Serum pregnenolone, progesterone, 17-hydroxyprogesterone, testosterone and 5α-dihydrotestosterone concentrations were measured radio-immunologically from a group of 200 normal girls 7–17 years of age. Samples from postmenarcheal girls were taken on days 6–9 and 20–23 of the menstrual cycle. Steroid concentrations were related to bone age, breast and pubic hair developmental stages, and gynecological age. When the premenarcheal values and the values from postmenarcheal samples taken on days 6–9 were related to bone age, the concentrations of all the five steroids increased with advancing age. The first steroid to exhibit a significant rise was pregnenolone. This rise was first seen between the bone age groups 7.5 and 8.5 years. Testosterone was quite unchanged until 9.5 years of bone age, after which a steep increase took place until 12.5 years, the concentrations reached being 3.5-fold the initial level. Following menarche, which took place at 13.4 years of bone age in this series, a plateau was visible i...